View original topic: GL 4 or GL 5 - "Official Gear Lube Topic" Page: 1, 2, 3 ... 60, 61, 62  Next
type3dude Sat Jan 26, 2008 1:59 pm

Moderator summary
GL4 or GL5-MT1 are fine for all VW transmissions.

Details of GL5 "controversy" in this post below:

The MT1 designation, which almost all current GL5 fluids contain, eliminates any fear of using GL5.

Original post is below:
What is the difference? Is one better than the other? I am about to put GL 5 in my tranny. Is this bad good or does it really not matter. Thanks

esde Sat Jan 26, 2008 2:29 pm

Gl5 is not safe for yellow metals in the trans (brass-bronze alloys), Gl4 is. I'm not sure what you need for the T1 trans, but at least now you know the difference. Most of the older german transmissions I've worked on specified Gl4, so you might go that way just to be safe. SD

Mudcat Sat Jan 26, 2008 3:14 pm

I added Amsoil 80W-90 GL5-MT1. J at sells it and he wouldn't sell a half ass product. There are alot of people running the MT-1 including Glenn if I remember right with no probs. John would not sell you crap. Notice that the Amsoil does not contain the additives others have.

Glenn uses Swepco but if its MT-1 regardless of brand it is not an issue.

Glenn Sat Jan 26, 2008 4:04 pm

esde wrote: Gl5 is not safe for yellow metals in the trans (brass-bronze alloys), Gl4 is.

Untrue.. welcome to the 90's, GL5 is perfectly safe and i've used iy for years.

Bruce Sat Jan 26, 2008 4:22 pm

esde wrote: Gl5 is not safe for yellow metals in the trans (brass-bronze alloys), Gl4 is.
That is an ancient myth, let it die. GL-5 is perfectly safe in your gearbox.
The reason older German transmissions specified GL-4 is because that is all that existed 30 year ago.

esde Sat Jan 26, 2008 4:48 pm

Glen and Bruce,
I don't claim to be an expert on this, But, there is a ton of info on the differences between GL4 and GL5 on a Benz website that I frequent.
There are literally hundreds of posts on the subject, the general consensus there is that GL5 has can have additives known to attack yellow metals. This is a big deal inearly transmissions that used some bushings instead of bearings. People that have run nothing but GL4 have had no trouble (almost), though others that have tried GL5 have mostly had trouble. This is especially true for early (60-70) unimog transmissions. Someone did post some correspondance with a tech from castrol, and they confirmed this.
A brief discussion about 4 vs 5 and the differences of hypoid vs non hypoid can be seen here.
Correct me if I've posted something incorrect, as I have researched this quite a bit.

type3dude Sat Jan 26, 2008 4:53 pm

I used the GL5 because the tranny was rebuilt very recently and It seemed like a good idea. I can always drain it again if need be. :lol:

Bruce Sat Jan 26, 2008 9:09 pm

esde wrote: Glen and Bruce,
.....though others that have tried GL5 have mostly had trouble. ....
What kind of "trouble"? Post your pics of damaged brass parts from using GL-5.

Go to your link:

Read the last post. All GL-5 gear oil you can buy today has the MT-1 rating, making it safe for brass.

If it was a real problem, there would be a warning label on the oil, warning you not to use it with brass parts. No such labels exist on any gear oil.

glandnut Sun Jan 27, 2008 10:32 am

Here's an explanation Bruce sent me almost 2 years ago when I had the same question. Figured I'd help you not to repeat yourself again, great info!

Jeff, All cars made today have brass syncros that look the same as Beetle syncros. To think that the oil companies would make a product that would destroy every gearbox it went into is rediculous. When I first heard this GL-4/GL-5 corrosion thing, I did some research on the oil co web sites. I couldn't find anywhere that said it was harmful, so I sent a tech message to the Amsoil tech guy. His response stated the history of how that myth got started by the ignorant VW people. When GL-5 first came out it was indeed corrosive to brass syncros. But only at temps above 250ºF. Now since it is impossible to get any street driven gear oil to that temp (It is hard to get engine oil that hot!), there will be no problems using regular GL-5. However, just to satisfy the ignorant masses, the API came up with another added rating, called MT-1 which is tacked onto the end of all GL-5 oils you can buy today. With this MT-1, GL-5 oil is not corrosive at any temp.
The difference between GL-4 and GL-5 is the extreme pressure capability. On surfaces that have high pressure where metal to metal contact will happen, the GL-5 is way better at protecting. Spider gear teeth and side gear teeth are one place where GL-5's better EP rating is desperatly needed. I've got 5-6 Bus 091 ZFs in my garage right now that have suffered significant wear on the gear teeth from probably using GL-4.
The nay-sayers like to point out their Bentley recommends GL-4. Of course it does, that's all there was 30 years ago. It also recommends using only mono-grade engine oil, bias ply tires........
The use of synthetic or dino makes no difference. I highly recommend you use syn over dino, you can really feel the difference in the way it shifts. If you buy a fresh gearbox, first put in dino for about 500-1000 miles then dump it and put in syn. It stays there long enough to warrant the extra cost, unlike syn engine oil.
I put my money where my mouth is. My last gearbox was a full out Berg 5 with close 2nd and a near NOS ZF. You couldn't pay me enough to risk damaging it with GL-4's inferior EP performance. Argueably, that gearbox is worth $3500-4k.
I always challenge the guys that say GL-5 is bad by asking them to tell me who do they know that had a failure using GL-5. Still waiting.
Good luck,

Glenn Sun Jan 27, 2008 10:36 am

I hope this put the debate to rest.

If you have proof that GL5 will damage a VW transaxle... post it up with pictures.

sammyphsyco Sun Jan 27, 2008 10:43 pm

I'm with Glenn & Bruce on this. I work as a Diesel mechanic and have never seen a yellow metal failure due to GL5. These transmisions typically have at least 200,000 miles. Failures are typicaly drivers who can't time their shifts.

jakecycle79 Mon Jan 28, 2008 3:57 pm


This debate exists in the BMW motorcycle world too.

I still don't know who to believe... :?

GL-5 has never ever failed me though.

nikita Tue Feb 26, 2008 3:13 pm


From Mazda to Getrag, Ive seen the inside of modern manual transmissions that do not use yellow metal synchros. And, since ATF or special fluids, not GL-4/GL-5/MT-1 are recommended in all modern passenger car and light truck owners manuals, the oil companies are only concerned with ring and pinion drive axles.

MT-1 is for heavy duty truck transmissions, without yellow metal syncros. Does MT-1 include a copper-strip corrosion test, like API motor oil? If it does, then I will stop debating the corrosion issue.

I dont understand the reference to spider and side gears. Those are not high tooth pressure gear profiles, nor are they loaded heavily compared to other gears in the transaxle.

Eding debate based on a two year old post, because we are "ignorant masses" is just a bit insulting. I think this website is above that sort of thing. I disagree with Glenn and others on just a few technical subjects, but never to insult him or anyone else.

BTW, I agree with your take on dino vs syn.

Bruce Thu Feb 28, 2008 12:26 am

nikita wrote:
I dont understand the reference to spider and side gears. Those are not high tooth pressure gear profiles, nor are they loaded heavily compared to other gears in the transaxle.
The severe wear I see all the time on VW diff gears tends to disagree with you.

Post your pics of syncros eaten away by using GL-5.

miniman82 Thu Feb 28, 2008 4:29 am

Bruce wrote: nikita wrote:
I dont understand the reference to spider and side gears. Those are not high tooth pressure gear profiles, nor are they loaded heavily compared to other gears in the transaxle.
The severe wear I see all the time on VW diff gears tends to disagree with you.

Post your pics of syncros eaten away by using GL-5.

They may not be high pressure gear profiles, but that does not take away from the fact that on a 2 spider diff, each spider will bear 1/2 of the power going to the ground when travelling in a straight line. Your statement that they are not heavily loaded is misguided, to say the least. On the other hand, you might say they take more abuse than any other gear in the trans, because any time the wheels are turning, so is the diff and it's spiders (to an extent). I've seen spider gear wear almost halfway through their respective shafts, that's not evidence of heavy loading??? C'mon man, you know a little more about transaxles than that, don't you?

Stuggi Sun Mar 23, 2008 3:54 pm

I just used synthetic 80W-90 in mine, Mobil 1 über-formula of ultra-doom or something along the crap they write on their cans. Worked like a charm, gears engage even better than before (and I was quite content with the old oil :D) and it's no longer stiff in cold weather.

nikita Tue Mar 25, 2008 1:12 pm

After reading this

I feel more comfortable with Castrol Hypoy C (the only non-synthetic that passed all tests) in my transaxle. While it is an Amsoil doucument, it appears to be relatively fair and honest. Note the copper strip corrosion test on page 17. Royal Purple and Lucas seem to have a problem. This is even though Royal Purple claims GL-4 and MT-1 as well as GL-5.

visibleink Sat Apr 12, 2008 1:25 pm

When I got my first bus there was a huge debate going on on GL4/5 on the type 2 list and GL4 won back then.

I still run GL4 to this day, I know alot of folks say it doesn't matter but I have about 15K miles on my rebuilt transmission and I only put GL4 (Stalube from NAPA) in it.

Ratwells argument pro-GL4:

Arnolds64 Mon Jun 02, 2008 3:21 pm

I bought a trans for my MX6 V6 that the guy had drained before selling. I bought the Valvoline GL5 Synthetic and used that even though I had read that GL4 was spec thinking like everyone that it does not matter. Driving it after replacing the Broken trans it was very notchy and if I shifted quick or downshifted to 2nd from 3rd it would slightly grind. Of course it was used and the guy said it did not grind when I bought it. I am pissed thinking the Synchros are bad and I got ripped off. Front wheel drive tranmission changes are not easy in your garage. I consulted and they recommended various types but said they needed to be GL4. I bought Red Line synthetic MT-90 and 1 bottle of MTL - 75-90 in this combo they suggested. I am here to tell you that it was like I put new synchros in and this did not depend on Temp either. Buttery Smooth! There is a difference. The GL4 is meant to work with the Brass or yellow metals and I guess this is in all the old transmissions. At only a few quarts, what is 10.00 each if it works well and for your piece of mind?

Kommercial Thu Jun 05, 2008 8:24 am

Everytime this topic comes up I am reminded of an interesting tag that comes with all transmissions from -
German Transaxle of America, formerly Volkstrans
61560 American Lane
Bend, OR 97702

"CAUTION! This trans must be filled with only 80 or 90 weight GL-4 Rated
oil, NOT GL-5, NOT GL-6, NOT GL-3-4-5, NOT GL 4-5-6! Use of any oil
other than straight GL-4 voids the warranty on the synchronizers! GL-4
oil is available from Pennzoil, Valvoline, Castrol, and many other
manufacturers. Do not be talked out of GL-4 by your local supplier who
may not have it! VW and Audi synchros were designed for GL-4 oil, and
any use of GL-5 will cause hard shifting and possibly damage to the
unit. Really! Trust us on this one.

We also highly recommend Redline MT-90 synthetic for easier shifting.
This is the only oil other than the correct GL-4 that will not void the
warranty on the trans."

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